This invention relates generally to optical networks. More particularly, the present invention relates to increasing a number of information channels carried by optical waveguides within an optical network.
In recent years, the use of optical fibers has become increasingly widespread in a variety of applications. Optical fibers have been found to be especially useful for many industries such as telecommunications, computer-based communications, and other like applications.
For example, in the conventional art as illustrated in FIG. 1, a long-haul network 10 connects central offices or points of presence (PoPs) 20 of one city to another. The long-haul network 10 typically utilizes optical waveguides, such as fiber optic cables, that carry information propagating in the 1550 nanometer wavelength region. The long-haul network 10 can interconnect major population areas together. For example, if the central office 20 that connects to the long-haul network 10 was part of a regional hub such as Atlanta, then the central office 20 would have long-haul fiber optic cable routes to Dallas, Chicago, New York, and other major population areas. The long-haul network 10 can be maintained by interexchange carriers (IXCs), such as ATandT, MCI, Sprint, and other like new companies that handle long distance communications.
Each central office or point of presence (PoP) 20 is interconnected to an adjacent central office 20 by optical waveguides 30 that form an interoffice network 40. An interoffice network 40 can be maintained by a local exchange carrier (LEC) such as Bell South, Bell Atlantic, and other companies that handle local communications. Each central office 20 of the interoffice network 40 can also be connected to optical waveguides 50 that form an access network or ring 70. Within an access network or ring 70, each central office 20 can be connected to one or more users 60. A user 60 can comprise local area networks (LANs) that provide services to individual personal computers or voice communications. Each access network 70 may extend across a geographic region on the order of 10 miles (more or less) in circumference, while the interoffice networks 40 may span a geographic region that is in the order of 50 to 100 miles (more or less) in circumference.
Because of the relative size of the access networks 70, communication providers typically employ synchronous optical network (SONET) standards for multiplexing and transporting data streams through the optical waveguides 50. The SONET standard is based upon a time division multiplexing (TDM) technique. However, despite the use of the time division multiplexing technique, conventional access networks 70 are approaching bandwidth exhaustion due to the demand created by the public Internet and/or virtual private intranets. Conventional access networks 70 are typically designed as optical carrier 3 (OC3) SONET rings meaning that the maximum capacity at any point in the optical waveguides 50 that form the access networks 70 have a capacity of 155 megabits per second. OC3 SONET rings can carry only three DS3 signals or eighty four DS1 signals on a entire ring. DS stands for a classification of transmitting one or more communications in a digital data stream. A DS1 level means that data is transmitted at 1.544 megabits per second while DS3 signals transmit data at 45 megabits per second. Users 60 are pressuring access network providers to support data transmitted at DS3 or higher rates as opposed to DS1 rates because current LANs operate much faster than DS1 streams.
To increase capacity of conventional optical networks, such as to accommodate eighty five DS1 signals or a fourth DS3 service, an entire OC3 SONET ring or access network 70 would require an upgrade to the optical carrier 12 (OC12) level that permits a maximum transmission capacity of 622 megabits per second at any point in an optical fiber. Such an upgrade would require complete replacement of add/drop multiplexers (ADMs) 220 (See FIG. 2) in the ring with larger capacity units.
Adding to the complexity of an upgrade to the SONET ring 70A is the current reliance by the industry on the unidirectional path switched ring (UPSR), as illustrated in FIG. 2. The UPSR 70A is a SONET architecture that is particularly well-suited for access networks 70 in which traffic from multiple users 60 is hubbed into a network provider""s central office or a point of presence (PoP) 20. The UPSR 70A includes fiber pairs 200, 210 that link multiple SONET add/drop multiplexers (ADMs) 220B-220E located at central offices/PoPs 20 and at remote locations accessible to users 60. Traffic, in the form of DS1 or DS3 serial data bit streams originating from each user 60, is multiplexed into the UPSR aggregate bit stream along optical waveguides 200, 210 at OC-3 or OC-12 data rates for transport to the central office or point of presence (PoP) 20. For example, a user 60D typically xe2x80x9caddsxe2x80x9d an information signal to the aggregate data bit stream propagating along the outside optical waveguide 200 via the transmitter 220T1. Similarly, the user 60D xe2x80x9cdropsxe2x80x9d an information signal from the aggregate data bit stream propagating along the outside optical waveguides 200 via the receiver 220R1.
Information traffic normally flows in one direction around the SONET ring 70A, using the working fiber 200 as indicated by the arrows denoting counter-clockwise flow. In the event of a single fiber or ADM transceiver failure, the information traffic is automatically redirected around the SONET ring 70A, using a protection fiber 210 in accordance with the UPSR automatic protection switching (APS) feature. For example, if two optical waveguides between two ADMs 220 simultaneously fail at points 240, such as optical waveguides 200 and 210 between user 60D and user 60E, then the UPSR APS feature will cross-connect the remaining working and protection fibers 200, 210 to bypass the failed sections in order to maintain continuity of information flow at each user""s connection. Therefore, instead of user 60D xe2x80x9caddingxe2x80x9d and xe2x80x9cdroppingxe2x80x9d information signals from the working optical waveguide 200, the user 60D would xe2x80x9caddxe2x80x9d signals to the working optical waveguide 200 via transmitter 220T1 and xe2x80x9cdropxe2x80x9d information signals from the protection optical waveguide 210 via the backup receiver 220R2 as illustrated in FIG. 2.
The robust protection switching capabilities of the UPSR make this SONET architecture preferable to other conventional topologies, such as star and tree-branch topologies for high availability fiberoptic access networks. With this protection scheme, a central office or point of presence (PoP) 20 would xe2x80x9creceivexe2x80x9d or xe2x80x9cdropxe2x80x9d information signals with the primary receiver 220R1 and transmit or xe2x80x9caddxe2x80x9d information signals to the SONET network 70A via the backup or secondary transmitter 220T2. It is noted that the xe2x80x9cworkingxe2x80x9d fiber 200 and xe2x80x9cprotectionxe2x80x9d fiber 210 may not be dedicated lines. In other words, the APS feature of an USPR may comprise complex switching techniques where a xe2x80x9cworkingxe2x80x9d or xe2x80x9cprotectionxe2x80x9d fiber is merely an optical path within an optical fiber that is a result of the complex switching techniques. The working fibers 200 and protection fibers 210 have been denoted as such in FIG. 2 for illustrative purposes only. That is, protection fibers 210 of FIG. 2 may carry information continuously while only an optical path generated by a switching technique is dedicated within the protection fiber 210 for the APS feature.
While the automatic protection switching feature of a unidirectional path switched ring makes a SONET architecture very desirable and dependable, such an optical architecture still suffers from signal losses that are present in any optical architecture. In order to compensate for such signal losses, amplifiers may be needed within each respective optical network 70A. However, conventional optical amplifiers, such as Erbium Doped Fiber Amplifiers (EDFAs), only operate in the 1530-1560 nanometer wavelength range. That is, conventional optical amplifiers are not designed to function within the 1310 nanometer wavelength range of interoffice networks 40 and access networks 70.
Accordingly, a need in the art exists for a method and system that can amplify optical signals propagating at various wavelength regions. More specifically, there is a need in the art for an optical amplifier that can be utilized in interoffice networks, access networks, and well as long haul networks. An additional need in the art exists for a method and system for increasing a number of information channels that can be carried by an optical waveguide. There is a further need in the art for a method and system for increasing a number of information channels carried by an optical waveguide that can be readily adapted or configured to work with existing optical network architectures. That is, there is a need in the art for a method and system that can increase a number of information channels carried by an optical waveguide but where an existing SONET architectures or SONET protocol is not affected by the increase in information channels. Specifically, there is a need in the art for a method and system that can substantially increase information traffic carried by an optical waveguide but can still retain the benefits of an automatic protection switching feature of a unidirectional path switched ring. Another need exists in the art for a method and system that can increase information traffic carried by an optical waveguide at relatively low cost with out replacing existing optical equipment and in a way where spare parts can be easily manufactured.
The present invention solves the problems of conventional optical networks by providing an optical add/drop multiplexing (OADM) device that can increase the number of information channels carried by an optical waveguide. The OADM device can increase the number of information channels within an optical waveguide by utilizing different wavelength regions of light. In other words, each information channel can be assigned a specific wavelength region of light. It is noted that a xe2x80x9cwavelength regionxe2x80x9d can be defined as a span of wavelengths that is adjacent or approximate to a specific wavelength. In other words, a wavelength region of xcex1 can include neighboring wavelengths of a desired threshold. For example, if it is desirable to have a threshold of one-fourth, a wavelength region of xcex1 could encompass wavelengths that are 0.25 below and above the central wavelength of xcex1. The threshold can be adjusted depending upon the application of the present invention.
By carrying information on multiple wavelength regions of light, the present invention can add virtual optical waveguides to existing physical optical waveguides. Stated differently, the present invention can carry information along information channels equivalent to separate dedicated physical optical waveguides that could be added to existing optical network systems. The OADM device can add additional virtual optical waveguides equal to the number of wavelength regions of light that can be efficiently propagated along a single optical waveguide. This means that if an optical waveguide can propagate twelve different wavelength regions of light, then an optical waveguide propagating light energy in this fashion would be equivalent to twelve separate conventional waveguides that could each carry a single wavelength region.
The present invention has an architecture such that it can be overlayed on conventional optical networks with minimal hardware or retrofitting or both. The invention can create additional optically transparent paths that permit the use of conventional optical network terminals. For example, the present invention can be easily interfaced with terminals designed for Synchronous Optical NETworks (SONETs). Further, the OADM device permits functionality of a conventional optical network to remain the same or constant.
In other words, if a conventional optical network, such as a SONET ring, has a protective switch capability where a protection optical waveguide is used if a working optical waveguide is broken or incapable of handling its information traffic, then such a protective switch capability would operate similarly as if the OADM device was not present. Stated simply, the present invention can be overlayed on conventional optical network systems such that an information channel operating according to a conventional network protocol is unaffected. Meanwhile, the present invention provides additional channels that do not need to be dependent on the conventional optical network protocol.
In addition to providing multiple channels that can be independent of a conventional network protocol, the present invention can utilize conventional protection optical waveguides for regular information traffic to increase the number of optical paths that lead to a central office or optical network service provider. That is, by utilizing conventional protection optical waveguides that exist in conventional optical network structures, such as SONET rings, the number of paths that lead to a central office can be doubled. For example, if a user is assigned an non-SONET information channel of a particular wavelength region and if two conventional optical waveguides of a SONET UPSR are utilized for information traffic, then the assigned non-SONET information channel for the user can have two bidirectional information routes that lead back to a central office.
With the present invention, information channels that propagate at predefined wavelength regions and that are unassigned at a particular terminal can be passed through a terminal with little or no energy loss. That is, the OADM device uses cascading technology that lets unwanted or unassigned information channels to pass through a terminal with minimal hardware. Conversely, conventional multiplexing technology typically requires a plurality of separate optical waveguides that are later recombined into a single optical device. Unlike the conventional multiplexing technology, the present invention has less hardware which, in turn, decreases the potential for any insertion losses.
The OADM device can utilize conventional diode laser technology for adding information channels at predefined wavelength regions into an optical network. In other words, the OADM device can stabilize the output wavelength region of a conventional laser diode to any specific wavelength region with minimal hardware or structural modifications. By utilizing off the shelf hardware, the OADM device can lower manufacturing costs while providing an ample supply of spare parts. Further, the same technology of the OADM device that increases the operating wavelength spectrum of conventional laser diodes can be used to amplify optical signals that propagate along the improved optical networks of the present invention. This dual functionality of the OADM device can further decrease its manufacturing costs.
The structure and functionality of the OADM device contribute to an efficient electronic packaging design. Each OADM device yields to an efficient field configurable unit that can be easily installed or replaced or both at a particular terminal. For example, each OADM device can be designed to add or drop (or add and drop) only one channel of a specific wavelength region. A terminal can include two OADM devices, one for each fiber of a two fiber network ring. Each OADM device may be configured with one or more wavelength adapter modules (discussed below) depending upon the number of information channels that will be handled by a particular terminal. That is, if a terminal is designed to operate on four wavelength regions, then four wavelength adapter modules can be installed within each OADM device for that terminal.
Each OADM device can comprise a wavelength adapter module and a filter module. Each wavelength adapter module can comprise a photodetector, a laser diode, and a Bragg grating. The Bragg grating can be combined with an optical waveguide. That is, the Bragg grating can be disposed within or adjacent to the optical waveguide. Each wavelength adapter module can be connected to a respective filter module that includes a planar light guide circuit and one or more optical waveguides and thin film interference filters. Each wavelength adapter module can be designed to modulate an incoming optical signal at a predefined wavelength region.
In one exemplary embodiment, the OADM device can drop one or more specific information channels operating at predefined wavelength regions at a terminal. In such an embodiment, the output ports of a filter module can be connected to input ports of a telecommunication device or computing device.
In another exemplary embodiment, the OADM device can amplify one or more specific information channels operating at predefined wavelength regions. In this embodiment, the output ports of a filter module can be redirected to the input ports of respective wavelength adapter modules. The wavelength adapter modules can, in turn, amplify the optical energy present at their input ports.